In the past, mechanical interlocks have been provided for off-road utility vehicle park brakes to link together the park brake and throttle pedal. For example, U.S. Pat. No. 3,912,056 relates to a mechanical interlock activated by the park brake to restrict the operator's ability to apply the throttle pedal. Fuel supply interlocks also have been proposed for use with park brake systems to disable the fuel supply if the park brake is applied. For example, U.S. Pat. No. 4,295,540 relates to a vehicle brake and engine interlock that suppresses power output at the engine if the park brake is engaged, such as by adjusting the throttle valve of a carburetor to stall or shut down the engine.
Other interlocks for park brake systems have been designed to prevent engagement or maintain or establish a neutral condition of a vehicle transmission while the park brake is engaged. For example, U.S. Pat. No. 4,051,915 relates to neutral start and park brake safety interlock circuitry that stops current to the ignition coil if the transmission is engaged in forward or reverse while the park brake is also engaged. U.S. Pat. No. 6,886,677 relates to a mechanism that locks the forward and reverse pedals in a neutral position while the park brake is engaged. U.S. Pat. No. 6,279,937 relates to a neutral return mechanism that will place the transmission in neutral while the park brake is applied.
Some park brake systems require an electronic engine controller having internal logic to limit the engine rpm while the park brake is engaged. However, an engine controller may be too costly for a utility vehicle park brake.
An interlock circuit is needed for a utility vehicle park brake that is low in cost and complexity. An interlock circuit is needed for a utility vehicle park brake that prevents vehicle travel without shutting down the engine. An interlock circuit is needed for a utility vehicle park brake that prevents vehicle travel while allowing the operator to shift the transmission into forward or reverse. An interlock circuit is needed for a utility vehicle park brake that is not subject to wear of mechanical parts.